The domain structure in thin films of an immiscible polystyrene/poly(methyl methacrylate) (PS/PMMA) blend was studied after spin-casting from a common solvent. Atomic force microscopy (AFM) combined with selective dissolution was used to obtain three-dimensional information on the domain morphology in thin films. Three different common solvents and three different substrate surfaces were studied. Distinct differences in the thin film domain structure and surface topography are observed depending on the substrate surface energy and the solubility of the two polymers in the three solvents. The topographic modulation can be explained by a different rate of solvent evaporation during spin-coating for the two phases. The normal and lateral organization of the phase-separated domains is governed by a complex interplay between preferential aggregation of one phase at the substrate and phase segregation in the film. Additionally, some of the results suggest that a dewetting process may be involved in the domain f...

Structure formation via polymer demixing in spin-cast films

Small-angle neutron scattering (SANS) has been used to investigate the conformation of linear and cyclic poly(dimethylsiloxane)s (PDMS) in chemically identical, undiluted blends. SANS measurements have been carried out on (1) linear hydrogenous (H) mixed with linear deuterated (D) PDMS and (2) cyclic H mixed with cyclic D PDMS. The conformational behavior of the cyclic and linear polymers is studied over a wide range of molar mass and composition. Isotopic blends of linear PDMS are shown to adopt conformations that agree well with theoretical predictions for Gaussian random-coil polymers and confirm previous SANS studies. As expected for chains obeying Gaussian statistics, the mean radii of gyration, Rg, scale with the weight-average molar mass as Rg ∝ Mw0.5. A detailed study of H/D cyclic PDMS mixtures is presented, and we demonstrate that, since Rg ∝ Mw0.4, highly flexible cyclic polymers in the melt adopt an even more compact conformation than that of unperturbed rings. This behavior confirms previous ...

Conformation of Cyclics and Linear Chain Polymers in Bulk by SANS

Before the application of small-angle neutron scattering (SANS) to the study of polymer structure, chain conformation studies were limited to light and small-angle x-ray scattering techniques, usually conducted in dilute solution owing to the difficulties of separating the inter- and intrachain contributions to the structure. The unique role of neutron scattering in soft condensed matter arises from the difference in the coherent scattering length between deuterium (bD = 0.67 × 10−12 cm) and hydrogen (bH = −0.37 × 10−12 cm), which results in a marked difference in scattering power (contrast) between molecules synthesized from normal (hydrogeneous) and deuterated monomer units. Thus, deuterium labelling techniques may be used to 'stain' molecules and make them 'visible' in the condensed state and other crowded environments, such as concentrated solutions of overlapping chains.For over two decades, SANS has proved to be a powerful tool for studies of structure–property relationships in polymeric systems and has made it possible to extract unique information about their size, shape, conformational changes and molecular associations. These applications are now so numerous that an exhaustive review of the field is no longer practical, so the authors propose to focus on the use of SANS for studies of strongly interacting soft matter systems. This paper will therefore discuss basic theory and practical aspects of the technique and will attempt to explain the physics of scattering with the minimum of unnecessary detail and mathematical rigour. Examples will be given to demonstrate the power of SANS and to show how it has helped to unveil universal aspects of the behaviour of macromolecules in such apparently diverse systems as polymer solutions, blends, polyelectrolytes and supercritical mixtures. The aim of the authors is to aid potential users who have a general scientific background, but no specialist knowledge of scattering, to understand the potential of the technique and, if they so choose, to apply it to provide new information in areas of their own particular research interests.

http://iopscience.iop.org/article/10.1088/0034-4885/68/8/R02/pdf

Recent applications of small-angle neutron scattering in strongly interacting soft condensed matter

Interfaces formed or exposed by polymer mixtures are often employed in modern technological applications. This is especially true for thin polymer films used nowadays in photoresist lithography, electrooptical devices or nanometer-scale surface patterning. Apart from these technology-oriented aspects the interfacial phenomena in thin polymer films pose a fundamental scientific challenge to physics of polymers and thermodynamics of condensed matter. This work reviews experimental results on the equilibrium properties of interfaces created by polymer mixtures confined in thin films. It confronts experimental data with theoretical expectations based mainly on mean field models. Most of the data have been obtained by high resolution profiling techniques emerged in the last decade. These techniques allow us to trace concentration vs depth profiles across a thin film with a depth resolution better than the characteristic size of a polymer coil. The interfacial phenomena of phase coexistence and segregation are described as observed in thin polymer films. This work also considers related issues in the focus of current research such as wetting phenomena, finite size effects expected in very thin films, surface (and bulk) properties of mixtures with stiffness disparity and conformational properties of end-segregated macromolecules forming polymer brushes.

Interfacial Phenomena in Thin Polymer Films: Phase Coexistence and Segregation

A series of symmetric poly(4-tert-butylstyrene-block-methyl methacrylate) (PtBS-b-PMMA) diblock copolymers with varying molar masses and narrow molar mass distributions were prepared using sequential anionic polymerization. Order-to-disorder transition (ODT) temperatures were determined as a function of the overall degree of polymerization, N, using a combination of low-frequency dynamic mechanical spectroscopy (DMS) and variable temperature small-angle X-ray scattering (SAXS), leading to a mean-field expression for the segment–segment interaction parameter, χ = (41.2 ± 0.9)/T – (0.044 ± 0.002). This material is characterized by a larger value of χ, and much greater temperature sensitivity, than polystyrene-b-PMMA, providing access to tunable lamellar periods (pitch) down to 14 nm at technologically relevant temperatures. Nucleation and growth of lamellae, following cooling from the disordered state, was characterized by SAXS well above the glass transition temperature (Tg ≈ 130 °C) and extrapolated to lo...

Synthesis, Thermodynamics, and Dynamics of Poly(4-tert-butylstyrene-b-methyl methacrylate)

For the isotopic blend of polystyrene (PS) PS/deutero PS (M=106 dalton), the Flory–Huggins interaction parameter χ(φ,T) was determined by means of the structure factor S(Q) measured by small angle neutron scattering (SANS). From χ(φ,T), the miscibility gap and the corresponding spinodal line was evaluated with a critical temperature of 130 °C. Decomposition in the miscibility gap is extremely slow due to the critical slowing down and due to a glass transition 30 K below Tc. Furthermore, the transition of the homogeneous blend between two temperatures was investigated by SANS. The interdiffusion constant of the two isotopic species was determined from these experiments. Our results approach the Cahn–Hilliard–Cook theory only in the limit of small wavenumbers of the fluctuations. Three weeks after annealing the sample, demixing was observed in the predicted two‐phase region.

Critical fluctuations and relaxation phenomena in the isotopic blend polystyrene/deuteropolystyrene investigated by small angle neutron scattering

The article deals with the phase diagram and spinodal decomposition of two polymers blends, namely d—PS/PVME and d(deutero)—PS/PS, investigated by small angle neutron scattering (SANS). The result of the static experiments is the excess free energy and the phase diagram. This is used as a basis for studies of non—equilibrium phenomena as spinodal decomposition. In polymer blends the Cahn—Hilliard—Cook theory of the early state of spinodal decomposition can be tested easily, because the blends have rather low relaxation rates; and they are meanfield systems [2,6] which makes interpretation simple, except in a very narrow temperature region near the critical point [6]. The kinetics in the isotopic blend d—PS/PS are so slow that the early states of spinodal decomposition can be studied within minutes. The presented SANS results have been performed at the KWS I small angle instrument at the FRJ—2 reactor in the KFA Julich.

Studies on the Excess Free Energy and The Early Spinodal Decomposition of the Blend d-PS/Peavrmley Asntda tteh Eof Isotopic Blend d-PS/PS with Small Angle Neutron Scattering

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Critical fluctuations and relaxation phenomena in the isotopic blend polystyrene/deuteropolystyrene investigated by small angle neutron scattering

Studies on the Excess Free Energy and The Early Spinodal Decomposition of the Blend d-PS/Peavrmley Asntda tteh Eof Isotopic Blend d-PS/PS with Small Angle Neutron Scattering